Russian President Vladimir Putin said he remained "positive" about the Syria cease-fire agreement struck with the United States last week but called for more transparency from Washington.

Putin, speaking in Kyrgyzstan's capital, Bishkek, on September 17 said he was "positive rather than negative" but said Washington needed to be "honest."

Moscow has accused Washington of refusing to share details of the closed-door truce agreement.

"They don't want to make it public because the world community... will understand who is really not abiding to what," Putin said.

He also accused opposition rebels fighting Syrian President Bashar al-Assad, a key Russian ally, of using the cease-fire to "regroup."

He claimed that Washington was facing a "difficult problem" in separating the rebels from terrorists, in reference to the opposition's ties with Jabhat Fateh al-Sham, formerly the Al-Qaeda-linked Al-Nusra Front, and Islamic State militants.

The United States and Russia cancelled a scheduled United Nations Security Council meeting on the cease-fire on September 16 as signs emerged that the truce was fraying.